The front face of a fuel injection nozzle is exposed to high temperature combustion gases that can reach temperatures as high as 2200 degrees C. Due to the extremely high levels of turbulence generated by swirl and primary zone jets, the heat transfer rates to the fuel injection nozzle tip are increased, it is important that the front face of the fuel injection nozzle tip be adequately cooled. Typical cooling techniques include convection and air-sweep cooling.
If a convection cooled fuel injection nozzle tip is cooled excessively, it tends to accumulate deposits of combustion generated carbon that can interfere with fuel atomization and dispersion, resulting in poor combustion efficiency and hot spots. If the injector is allowed to run at temperatures higher than 800 degrees C., failure of the front face can cause secondary damage to the combustor walls through oxidation, cracking, and buckling. The combustor exit temperature profile and pattern factor can deteriorate, resulting in damage to the downstream gas turbine components.
An example of past injection nozzles in which an attempt has been made to cool the front face is disclosed in U.S. Pat. No. 4,977,740 issued on Dec. 18, 1990 to Thomas J. Madden et al. The injection nozzle disclosed includes an air passage through which cooling air is directed into contact with the inside surface of a conical deflector portion of a conical deflector section. Thus, an attempt to cool the tip by convection at the inner surface is disclosed.
Another example of an injection nozzle attempting to cool a front face is disclosed in U.S. Pat. No. 4,798,330 issued on Jan. 17, 1989 to Alfred A. Mancini et al. Cooling air passes through an air swirl chamber and terminates in an outer air discharge orifice. A portion of the air exits an aperture in the front face and is used to attempt to cool the front face.
Another example of an injection nozzle attempting to cool a front face is disclosed in U.S. Pat. No. 4,600,151 issued on Jul. 15, 1986 to Jerome R. Bradley. The injection nozzle disclosed includes an air passage through which cooling air is directed into contact with the inside surface of a frusto-conical portion of a shroud member.
Another example of an injection nozzle attempting to cool a front face is disclosed in U.S. Pat. No. 3,866,413 issued Feb. 18, 1975 to Geoffrey J. Sturgess. Cooling air enters through a plurality of ports and cools the dome.
Another example of an injection nozzle attempting to cool a front face is disclosed in U.S. Pat. No. 3,684,186 issued Aug. 15, 1972 to William F. Helmrich. This patent discloses a secondary air swirl chamber formed by a portion of a shroud. The air exiting the chamber partially cools the front face prior to being mixed with fuel.
Another example of an injection nozzle is disclosed in U.S. Pat. No. 3,483,700 issued Dec. 16, 1969 to John G. Ryberg et al. The patent discloses a front face having a plurality of scoops formed therein. A mixture of fuel and air pass through the scoops into a combustion chamber. The mixture of fuel and air attempts to cool the front face.
Many attempts have been made to improve front face cooling and to extend the life of fuel injection nozzles. Experimentation has shown that it is difficult to achieve optimum front face temperature with both gaseous and liquid fuels over the complete range of loads and ambient conditions in a gas turbine engine. Thus, using convective cooling or air-sweep alone does not appear to solve the front face cooling problem. It appears that a combination of convective cooling and air-sweep cooling usually has better durability. This is due to the lower front face temperature and avoidance of carbon deposits by air-sweeping action.